5 This question is about ammonia, NH3.
5-1 Complete the dot and cross diagram for the ammonia molecule shown in Figure 6. Show only the electrons in the outer shell of each atom.
[2 marks]
Figure 6
ANSWER
Where,
“x” represent electron of Nitrogen
“ ”represent electron of hydrogen
5-2 Give one limitation of using a dot and cross diagram to represent an ammonia Molecule.
[1 mark]
ANSWER
Can give the impression that the structure is made of pairs of ions rather than being a continuous structure containing a massive number of ions;
OR
Can give the impression that the structure is limited to a few ions rather than being a continuous structure with a massive number of ions;
OR
Only shows the structure in 2D.
5-3 Explain why ammonia has a low boiling point.
You should refer to structure and bonding in your answer.
[3 marks]
ANSWER
Ammonia (NH3) has a low melting point and boiling point because of the nature of its chemical bonds. The molecules of ammonia are held together by hydrogen bonds, which are relatively weak intermolecular.
5-4 Ammonia reacts with oxygen in the presence of a metal oxide catalyst to produce box nitrogen and water.
Which metal oxide is most likely to be a catalyst for this reaction? [1 mark]
ANSWER
Cr2O3
Figure 7 shows the displayed formula equation for the reaction.
Figure 7
Table 3 shows some bond energies.
Table 3
5-5 Calculate the overall energy change for the reaction.
Use Figure 7 and Table 3.
[3 marks]
ANSWER
For bonds broken
For bonds made
Overall Energy Change
5-6 Explain why the reaction between ammonia and oxygen is exothermic. Use values from your calculation in Question 05.5
[2 marks]
ANSWER
7458 (kJ) is released in making bonds which is greater than 6186 (kJ) used in breaking bonds. Also, the products have 1272 (kJ) less energy than the reactants.
5-7 Figure 8 shows the reaction profile for the reaction between ammonia and oxygen.
Complete Figure 8 by labelling the:
• activation energy
• overall energy change.
[2 marks]
Figure 8
ANSWER
